FXC-5469 fix(tidy3d): add discriminator to simulation type union fields

[dmarek-flex]

Addresses FXC-5469: https://flow360.atlassian.net/browse/FXC-5469

Adds discriminated_union() to the values_tuple fields of SimulationMap and SimulationDataMap so pydantic v2 uses the type tag to select the correct union variant directly, preventing spurious ModeSimulation error logs during deserialization.

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Note

Low Risk
Type-annotation-only change to Pydantic model fields plus a regression test; main risk is unintended deserialization incompatibility for any union variants missing/incorrect type tags.

Overview
Prevents spurious ERROR-level logs during Pydantic v2 deserialization of SimulationMap/SimulationDataMap by switching their values_tuple fields to use discriminated_union(...), so union selection is driven by the type tag instead of trial-and-error validation.

Adds a regression test asserting SimulationDataMap round-trip validation emits no logs above WARNING, and records the fix in CHANGELOG.md.

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Test requires WARNING log that may not exist

Low Severity

AssertLogLevel("WARNING") requires at least one WARNING-level log to be present during the context. If the model_validate roundtrip doesn't emit any warning, the assertion framework raises an error at the "Log was not recorded but requested log level is not None" check. Every other usage of AssertLogLevel("WARNING") in the codebase pairs it with a specific contains_str to confirm a known warning exists. This test implicitly assumes warnings will be emitted, making it fragile to future changes that clean up validation warnings.

 

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Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/data/index.py (100%)
• tidy3d/components/index.py (100%)

Summary

• Total: 4 lines
• Missing: 0 lines
• Coverage: 100%